1. Field of the Invention
The present invention relates to the gallium-nitride based light-emitting diode, and in particular to the epitaxial structure of the gallium-nitride based light-emitting diode.
2. The Prior Arts
Gallium-nitride (GaN) based light-emitting diodes (LEDs) has been the research and development focus in the academic arena and in the industries in recent years. A conventional practice for the GaN-based LEDs is to use the multi-quantum well (MQW) structure in the GaN-based LED's active layer, which is interposed between barrier layers made of Si-doped GaN. The barrier layers effectively confine the electrons and holes inside the active layer and, thereby, increase the possibility of forming the electron-hole pairs inside the active layer. This in turn increases the internal quantum efficiency and decreases the operating voltage as well of the GaN-based LED. However, the Si-doped barrier layers also have a side effect. The Si-doped barrier layers would absorb a number of the photons released by the joining of the electrons and holes in the active layer of the GaN-based LED. This would apparently decrease the external quantum efficiency of the GaN-based LED. In addition, the conventional Si-doped barrier layers have significantly different lattice constants from that of the MQW active layer. Due to the piezoelectric effect, excessive stress would therefore be developed among the epitaxial structure of the GaN-based LED, causing the GaN-based LED to have inferior device characteristics.
Accordingly, the present invention is directed to overcome the foregoing disadvantages of conventional GaN-based LEDs according to prior arts.